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1911 Encyclopedia Britannica
(Lat. butyrum, Gr. rvpov, apparently connected with (30us, cow, and Tvpos, cheese, but, according to the New English Dictionary, perhaps of Scythian origin), the fatty portion of the milk of mammalian animals. The milk of all mammals contains such fatty constituents, and butter from the milk of goats, sheep and other animals has been and may be used; but that yielded by cow's milk is the most savoury, and it alone really constitutes the butter of commerce. The milk of the various breeds of cattle varies widely in the proportion of fatty matter it contains; its richness in this respect being greatly influenced by season, nature of food, state of the animals' health and other considerations. Usually the cream is skimmed off the surface of the milk for making butter, but by some the churning is performed on the milk itself without waiting for the separation of the cream. The operation of churning causes the rupture of the oil sacs, and by the coalescence of the fat so liberated butter is formed. Details regarding churning and the preparation of butter generally will be found under Dairy And Dairy Farming.
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Chisholm, Hugh, General Editor. Entry for 'Butter'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/b/butter.html. 1910.